Hi all,

I am currently having a problem, I am fitting a scatterplot with a second degree polinomial (written as [0]*x*(1+[1]*x) in order to have the second degree parameter in percentage). The problem is that the points are fairly precise and when I perform the fit it gives the right values of the parameters but the error on the parameters are of order 10^7 (basically 7 to 10 orders of magnitude bigger than the correct values). This error disappears if I multiply the incoming data with 10^6 in order to make the numbers bigger and then divide by this factor again.

Basically it looks like some kind of “underflow” error.

Worth mentioning is that I am performing the fit via pyroot using the standard fitting procedure of declaring the graph, the function and then call the Fit() method of the graph.

Is there any way I can fix this issue without doing this ugly multiplication? Is it a known issue in general?

Thank you,

Giorgio

_ROOT Version: 6.22

_Platform: linux